Yeah, that's true. I honestly don't know why either. It's all the same things- Period for female, period in this story, heat..it's just an amount of time to show that you can get a kid or something. I also found it unsettling at first, but it was because I read too many omegaverse.
Why can't they just call it a heat? It's not a big deal, but it's just weird to me that they're referring to the "heat" as the "period"